MEMS-based systems, including flat panel displays that exploit the principle of frustrated total internal reflection (FTIR) to induce the emission of light from the system, may have to satisfy crucial physical criteria to function properly. The display system disclosed in U.S. Pat. No. 5,319,491, which is incorporated by reference in its entirety herein, as representative of a larger class of FTIR-based MEMS devices, illustrates the fundamental principles at play within such devices. Such a device is able to selectively frustrate the light undergoing total internal reflection within a (generally) planar waveguide. When such frustration occurs, the region of frustration constitutes a pixel suited to external control. Such pixels can be configured as a MEMS device, and more specifically as a parallel plate capacitor system that propels a deformable membrane between two different positions and/or shapes, one corresponding to a quiescent, inactive state where FTIR does not occur due to inadequate proximity of the membrane to the waveguide, and an active, coupled state where FTIR does occur due to adequate proximity, said two states corresponding to off and on states for the pixel. A rectangular array of such MEMS-based pixel regions, which are often controlled by electrical/electronic means, is fabricated upon the top active surface of the planar waveguide. This aggregate MEMS-based structure, when suitably configured, functions as a video display capable of color generation, usually by exploiting field sequential color and pulse width modulation techniques.
The criteria to be satisfied for such MEMS-based FTIR systems to function properly may involve control over the shape of the membrane being electrically deformed during both activation and deactivation. The simplest MEMS structure normally selected for such implementation involves using opposing conductors configured so that the presence of a potential difference between them entails an imposed Coulomb attraction, causing relative motion of one or both of the conductors and any other materials tied to them. Such a system is traditionally termed a parallel plate actuator system, where one of the conductors is fixed, while the other is disposed on a member that is either capable of motion (generally being affixed at its putative edges by appropriate tethers or standoff layers) or elastic deformation to controllably close the gap between the fixed and moveable conductor regions.
The electromechanical behavior of a parallel plate actuator system is usually optimal when the plates in question (the conductive regions across which a voltage potential is applied to induce relative motion between them) are rigid, parallel planes. Their rigidity contributes to keeping the plates parallel, assuming an otherwise appropriate distribution of ponderomotive force and concomitant fixturing or tethering of both the fixed and moveable elements by which the plates are mounted. If, for example, the moveable plate is not rigid, but elastic, it is clear that during the actuation event for such a system, there will be moments in time when the plates are no longer parallel to one another, due to geometric deformation of the non-rigid moveable plate under the influence of ponderomotive forces that naturally distribute themselves to secure the lowest potential energy state at all times during actuation.
During an elastic deformation that causes the respective plates to deviate from a mutually parallel spaced-apart relation, the electromechanical parameters for system behavior shift in significant ways that are, in most cases, regarded as deleterious and harmful to proper and/or optimal MEMS operation. A means to recover the more desirable behavior associated with a double-rigid-plate system, in the context of a system where one of the plates is quite flexible and capable of significant elastic deformation, would restore the desired MEMS behavior while retaining the other known advantages accruing to a MEMS defined exploiting elastic deformation to implement controllable relative motion of the plates.
Therefore, there is a need in the art for a means to recover MEMS behavior associated with rigid, parallel plate actuator elements when one or more of the elements is not actually rigid but capable of deformation. A MEMS device that enjoys the electromechanical behavior profile associated with rigid plate interaction while actually being composed of one or more non-rigid plate structures would bring the benefits of both architectures (rigid and non-rigid) to bear on a single MEMS device structure.